<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style>
			#hd{
				width: 300px;
				height: 150px;
				background: dodgerblue;
				
				animation: run 3s infinite alternate;
			}
			
			
			@keyframes run{
				0%{
					width: 300px;
				}
				
				100%{
					width: 900px;
				}
			}
			
		</style>
	</head>
	<body>
		<div id="hd">
			
		</div>
	</body>
</html>
